vdpa net: follow VirtIO initialization properly at cvq isolation probing

vdpa net: follow VirtIO initialization properly at cvq isolation probing

This patch solves a few issues.  The most obvious is that the feature
set was done previous to ACKNOWLEDGE | DRIVER status bit set.  Current
vdpa devices are permissive with this, but it is better to follow the
standard.

Fixes: 152128d646 ("vdpa: move CVQ isolation check to net_init_vhost_vdpa")
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230915170836.3078172-4-eperezma@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 845ec38ae1578dd2d42ff15c9979f1bf44b23418)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>